Macroevolution






  • Microevolution happens at the population level (natural selection, genetic drift, gene flow)


  • Macroevolution: Speciation events form evolutionary independent populations


  • New species are the bridge between evolution within a population and larger patterns in evolution, such as new taxonomic groups

How/Why species form: The limits of human cognition


What actually is a “Species”?








  • Textbooks: A group of populations whose members have the potential to interbreed in nature and produce viable offspring

What actually is a “Species”?








  • Textbooks: A group of populations whose members have the potential to interbreed in nature and produce viable offspring

Biological Species Concept: Unity of reproduction



  • Reproductive isolation between populations results in a lack of gene flow
    • what are the consequences of no gene flow?


  • Individuals do not interbred with other populations or are unable to produce viable offspring after mating
    • pre- and post-zygotic barriers


  • BSC: Members of a biological species are united by the potential ability to be reproductively compatible

Mechanisms of reproductive isolation in Meadowlarks



Issues with the biological species concept




  • How do we effectively evaluate isolation?
    • Is this even possible in fossils?


  • Geographic proximity: how do we know if they cant make babies?


  • Asexual reproduction is unaccounted for…
    • Belloid rotifers haven’t reproduced sexually for > 80 million years
    • An estimated 2000 species of asexual rotifers are known

Morphological Species Concept: Unity of body plans


MSC solves issues with fossils and asexual organisms

Issues with the morphological species concept





  • Applies to all organisms but…. what kinds of traits & how many?
    • Subjective to the scientist!


  • Species can change their form: Polymorphisms


  • Cryptic species that do not differ in morphology
    • lots of mimics in nature!

Lineage Species Concept: Unity of ancestry


LSC uses genetic similarity/differences to determine species but is subjective in the magnitude of differences needed.

How new species arise: Allopatry


Allopatric speciation in Hawaiian fruit flies


Hawaiian islands form through time. Fruit flies from one population migrate to a new island (physical separation) and have formed many new species

Allopatric speciation in shrimp


The Atlantic and Pacific oceans used to connect before what we call Panama arose from the ocean. Different shrimp species live at different depths (colors on the picture). As Panama split the ocean these populations (by depth) became isolated and formed different species. The deep species (red) on opposite sides are more different than shallow species (green) because they have been separated longer!!

How new species arise: Sympatry


Sympatry in Hawthorn and apple flies


Study aid: The geography of speciation


The pre- and postzygotic barriers can form for either type of speciation